Conventionally, there has been an exemplary structure in which a clutch actuator is mounted to the outside of a crankcase of an internal combustion engine. In this structure, however, during the operation of the clutch actuator, the operating sounds generated at valve opening and closing times are transmitted to the exterior, which naturally is undesirable (see, for example, FIG. 3 of Japanese Patent Laid-open No. 2008-057620).
There has been another exemplary structure in which a clutch actuator is mounted to the inside of a crankcase. Also in this structure, however, sounds are echoed onto a thin clutch cover, again leading to leakage of operating sounds to the exterior (see, for example, FIG. 6 of Japanese Patent Laid-open No. 2008-138541).